Once you drop off the roof of the truck you rode through on, it's time to take out the Soviet guards. You can do this most easily using the .45 on the oil drums near the two guards. A few rounds as you sprint forward should take out the drums and the guards. There are at least two more guards waiting for you in this area, so be careful to take them out. Then go inside the room located between the two 21/2 ton trucks. In there, there is a block or a table. Climb up on it, line yourself up with the hole in the roof, jump through and grab on, then hoist yourself up to the next level. Once there, go out on the ledge and look for the staircase down. Then the level really gets hard.